1. Field of Invention
The present invention relates generally to an improved vessel configuration for high speed ships such as Naval Destroyers and, more particularly, to a vessel having a watertight hull with no penetrations therein for propulsion machinery wherein all main machinery is modular and is located outside the watertight hull.
2. Brief Description of Related Art
Ever since steam powered propellers replaced wind powered sails as the main means of propelling ships, the powerplant has occupied the center of the hull. The midship located powerplant has been connected by long, heavy shafts to aft mounted propellers. Steering has generally been provided by rudders aft of the propellers. From the middle of the nineteenth century to the present the overwhelming proportion of the world's surface combatants and cargo ships have shared this configuration.
The Great White Fleet of Teddy Roosevelt's era, the four stacked destroyers of World War I, and the entire World War II fleet are examples of such designs. Nuclear powerplants introduced into Naval cruisers and destroyers merely substituted for the boilers, fuel tanks, and turbines of their fossil-fueled predecessors.
When compact, aircraft-derivative gas turbines were introduced in the Spruance class destroyers in the seventies, the powerplant configuration was little changed from those preceding it. The Ticonderoga class cruisers of the eighties and the Arleigh Burke class destroyers of the nineties retain this same powerplant configuration. For surface combatants with maximum Froude Numbers exceeding 0.4, this configuration can cause the cost of the mechanical and electrical systems to exceed four times the cost of the hull structure.
For high speed ships, wavemaking resistance increases dramatically with speed. Resistance of a bare-hull can be divided into a viscous component and a wavemaking component. For ships at low speeds, viscous resistance predominates, whereas at sustained speed (speed at 80% of full power) and maximum speed (speed at full power), large wavemaking resistance is added. Wavemaking resistance is somewhat dependent on hull shape, heavily dependent on "fatness," and varies sharply with the dimensionless Froude Number [Fr=V/(gL).sup.0.5, where V is ship speed, g is the gravitational constant, and L is length at the waterline]. Wavemaking resistance is very small compared to viscous resistance at Froude numbers below about 0.34, but then it rises sharply so that at a Froude number of about 0.45, its value is several times that of viscous resistance. Furthermore, the open shafting of high speed Naval combatants typically adds 45% to the viscous resistance of the bare hull.
For displacement monohulls, to minimize the cost of the power systems, the hull should be long enough that the sustained speed is reached without wavemaking resistance becoming predominant. Preferably, the Froude number should not exceed 0.38 at sustained speed. In the past, the Navy design philosophy was that propulsion systems were preordained, of fixed cost and size, and that ship cost was best reduced by making the ship as short as possible. The 466 foot length Arleigh Burke class "short" destroyer represents the philosophy of trying to save cost by shortening the hull. However, shortening the hull increases Froude number, and thus wavemaking resistance, at a given speed. Increased resistance translates to increased power required for a given speed which, in turn, increases the fuel consumption over time. In addition, at a constant fuel capacity, ship resistance is approximately inversely proportional to ship range.
A conventional, prior art ship design having vertical topsides 10 is depicted in FIGS. 1-4. Centrally located powerplants 12 and propulsion shafting 14 are installed in the hull early in the overall ship construction process. As shown in FIGS. 3 and 4, powerplants 12 are generally located in one or more large main machinery rooms 16 that, along with required air intake ducting 18 and exhaust ducting 20, occupy a large volume near midships. It is prohibitively costly to remove and replace much of the main machinery systems once installed. Removing propulsion power generation machinery 22, propulsion transmission machinery (shafting 14 and gears 24), or ship-service electrical generation machinery 26 and 28 would require cutting large holes in the side of the hull. Consequently, these machinery systems are designed to have very low stresses and are thus exceedingly heavy and costly. Lightly loaded "safe" gears are a high weight legacy of this configuration. A second legacy is long, heavy shafting, which is costly to align. A third legacy is large air intake and exhaust ducting (in gas turbine powered ships, the air intake and exhaust uptake ducting are typically very large), which occupy much of the upper decks and superstructure. The weight and required space for shafting and ducting may add 50% to the weight and space requirements of the main electric and power producing machinery. Moreover, highly desirable spaces near the center of gravity of the ship, where ride motion is minimal, are dedicated to machinery and ducting, not to personnel living and working quarters. Furthermore, repairs are generally conducted in situ, often in inconveniently cramped quarters.
Further inefficiencies are introduced by the ship-service power generation machinery 26 and 28. Ship-service power (power other than propulsion power) has typically been produced by small turbines that operate at a low fraction of their design power and thus have net efficiencies near 15%. As a result, as much as one quarter of the fuel consumed at cruise speeds is used for "hotel loads" such as heating, ventilation, air conditioning, lighting, food and fresh water production, fire protection, i.e., non-propulsion related, ship-service power.
Moreover, hulls have customarily been designed for transverse stability and roll frequency at full-load displacement (full payload including full-fuel-load) with the required beam for stability being constant above the design waterline, i.e., vertical topsides 10 as shown in FIG. 1. To maintain transverse stability throughout the mission, ship hulls designed for stability at full-load require sea water ballast to compensate for expended fuel. In the past, as fuel was burned, sea water was pumped into the fuel tanks, and was then pumped out upon refueling. However, using emptied fuel tanks for ballast water increases pollutants discharged from the ship as "dirty" ballast is pumped into surrounding water. In accordance with international pollution control limits, future fuel tanks may not be ballasted by dischargeable water. The current Navy procedure is to build excess clean water ballast tanks. Excess ballast tanks, however, are wasteful of ship space, and carrying seawater increases fuel consumption late in the mission.
The price of the conventional prior art ship configuration is increased initial cost, increased fuel cost, and decreased capability. Consequently, there is a need to provide a more affordable, more capable, less polluting vessel. Such a vessel should use internal space more effectively than conventional vessels and should have adequate transverse stability without adding ballast as fuel is burned. The present invention is intended to overcome problems associated with prior art ship designs.